CuI-catalyzed tandem synthesis of thioethers using aryl halides,electron-deficient alkenes,and sodium iso-propyl xanthogenate

A ligand-free, CuI-catalyzed protocol was developed for the one-step preparation of Michael adducts of aromatic thiols in high yields by reacting a mixture of an aryl halide and an electron-deficient alkene with sodium iso-propyl xanthogenate.     

Non-singular Brans–Dicke collapse in deformed phase space

We study the collapse process of a homogeneous perfect fluid (in FLRW background) with a barotropic equation of state in Brans–Dicke (BD) theory in the presence of phase space deformation effects. Such a deformation is introduced as a particular type of non-commutativity between phase space coordinates. For the commutative case, it has been shown in the literature (Scheel, 1995), that the dust collapse in BD theory leads to the formation of a spacetime singularity which is covered by an event horizon. In comparison to general relativity (GR), the authors concluded that the final state of black holes in BD theory is identical to the GR case but differs from GR during the dynamical evolution of the collapse process. However, the presence of non-commutative effects influences the dynamics of the collapse scenario and consequently a non-singular evolution is developed in the sense that a bounce emerges at a minimum radius, after which an expanding phase begins. Such a behavior is observed for positive values of the BD coupling parameter. For large positive values of the BD coupling parameter, when non-commutative effects are present, the dynamics of collapse process differs from the GR case. Finally, we show that for negative values of the BD coupling parameter, the singularity is replaced by an oscillatory bounce occurring at a finite time, with the frequency of oscillation and amplitude being damped at late times.     

BSA optimization and dosimetric assessment for an electron linac based BNCT of deep‐seated brain tumors

A study was conducted to investigate a photoneutron spectrum based on a 25 MeV electron linac for treatment of deep-seated brain tumors in the context of boron neutron capture therapy (BNCT). Based on a series of Mont Carlo N-Particle simulations, tungsten and uranium with optimized geometry were selected as the most appropriate converters for (e,γ) and (γ,n) reactions, respectively. The final optimized photoneutron source yield was 5.78 × 10¹³ n/s/mA, which is a high value for these kinds of sources. A beam shaping assembly (BSA) for the proposed neutron source containing optimal moderators, filter, reflector, and collimator was simulated. Results showed that using this BSA enables us to meet International atomic energy agency recommended figures of merit at the BSA beam port. Also, the calculated in-phantom figures of merit and dose evaluation results via a simulated head phantom confirmed that the designed neutron source and its related BSA configuration can potentially treat deep-seated brain tumors in BNCT framework. In the present study, some in-phantom figures of merit such as advantage depth, advantage depth dose rate, advantage ratio, and treatment time are 7.6 cm, 0.7 Gy/min, 4.2, and 17.8 min, respectively.     

Synthesis, crystal structures and electrochemical properties of CoIII complexes with hexadentate ligand containing thioether-amidopyridyl donor set

Two new cobalt(III) complexes of the hexadentate ligand [1,4-bis[o-(pyridine-2-carboxamidophenyl)]-1,4-dithiobutane] (H₂bpctb) with N₄S₂ donor set atoms have been synthesized. A reaction of Co(CH₃COO)₂·4H₂O with (H₂bpctb) leads to the formation of [Co^III(bpctb)]PF₆ (1) having a CoN₂(pyridine)N′₂(amide)S₂(thioether) coordination by symmetric bpctb^2? ligand. A similar reaction under slightly different conditions, however, gives [Co^III(L ^a )(L ^b )] (2), resulting from a C–S bond cleavage reaction triggered by an acetate ion as a base, having CoN₂(pyridine)N′₂(amide)S(thioether)S′(thiolate) coordination. These two Co(III) complexes have been characterized by elemental analyses and spectroscopic methods, and the crystal and molecular structures of [Co^III(bpctb)]PF₆ (1) in the form of the solvate (1·MeOH·H₂O) and of [Co^III(L ^a )(L ^b )] (2) have been determined by X-ray crystallography. The Co atoms of both complexes exhibit distorted octahedral geometry. The electrochemical investigation of [Co(bpctb)]PF₆·MeOH·H₂O (1·MeOH·H₂O) and [Co^III(L ^a )(L ^b )] (2) by cyclic voltammetry reveals a reversible Co^III–Co^II redox process at E _1/2 = ?0.32 V (ΔE _p = 80 mV); for 1, and E _1/2 = ?0. 87 V (ΔE _p = 70 mV) for 2.     

Electromagnetic fields near plasmonic wedges

The behavior of electromagnetic fields near the edge of a plasmonic wedge is investigated. We study the scattering properties, field divergence, and field enhancement near an Au wedge bounded by SiO2 upon illumination by TM-polarized light using hypersingular integral equations, as a function of wavelength, wedge angle, and angle of incidence. The transverse scattered field components show a convergent behavior at wavelengths approaching the surface plasmon energy asymptote (on the corresponding flat Au-SiO2 interface), and become strongly divergent at longer wavelengths. The computed divergence is compared with Meixner's theory and is found to be in good agreement over a restricted range of parameters.     

The Nehari manifold approach for a class of n\times n nonlinear elliptic systems

In this paper, by analysis of the relationship between the Nehari manifold and fibering maps, we discuss the existence, multiplicity and nonexistence of positive weak solution for the $(p_1,p_2,\ldots ,p_n)$ -Laplacian systems with sign-changing weight functions.     

A theoretical analysis of the effects of erbium ion pair on the dynamics of an optical gain stabilized fiber amplifier

In this paper, the effects of ion-pair formation on the gain dynamics of multi cavity optical automatic gain control erbium doped fiber amplifier is modelled. The inhomogeneous Cabezas simple model is used to write the rate and propagation equations for the active medium. The solution of the governing equations shows that in high concentration of the erbium ions, depending on the pumping rate, the relaxation oscillations are converted to nT-Periodic or even to chaotic behavior. Although the high concentration erbium ion in the optical amplifiers decreases the conversion efficiency and increases the threshold pump power, amplitude of the transient effects is reduced in the multi feedback-loop WDM amplifiers relative to the low concentration erbium ions multi feedback-loop optical amplifiers and ion-pairs, which act as a saturable absorber to compensate the gain tilt caused by the OAGC laser spectral hole burning. The theoretical results are in complete agreement with the previous published experimental results.     

Preparation and characterization of polyurethane based self-cleaning and antibacterial coating containing silver ion exchanged montmorillonite/TiO<Subscript>2</Subscript> nanocomposite

In order to reach an antibacterial, photocatalytic, and hydrophilic coating, commercial grade polyurethane (CPU) resin was modified with silver ion exchanged montmorillonite/TiO₂ nanocomposite in various montmorillonite to TiO₂ nanoparticle ratios. To characterize the prepared nanocomposites and coatings, X-ray diffraction patterns, FTIR and UV–Vis spectroscopy and SEM images were used. The modified commercial grade polyurethane coatings containing nanocomposites show better properties, including hydrophilicity, degradation of organic pollutants, antibacterial activity and water resistivity, compared to unmodified commercial grade polyurethane coatings. The water droplet contact angle of unmodified CPU coating was 70°, however it decreased to lower than 10° in modified CPU coatings after 24 h LED lamp irradiation. Decolorization efficiency of malachite green dye solution by the use of modified CPU coatings achieved up to 70% after 5 h LED lamp illumination, compared to less than 5% for unmodified CPU coatings. Modified CPU coatings also showed significant water resistivity and antibacterial properties.     

One-pot synthesis of functionalized thioureas by reaction of benzoyl isothiocyanates, secondary amines, and alkyl propiolates

An efficient one-pot synthesis of functionalized thioureas is described via three-component reaction of benzoyl isothiocyanates, secondary amines, and alkyl propiolates in the presence of triphenylphosphine (20 mol%). Correspondence: Issa Yavari, Chemistry Department, Tarbiat Modares University, PO Box 14115-175, Tehran, Iran     

Application of the moiré deflectometry on divergent laser beam to the measurement of the angle of arrival fluctuations and the refractive index structure constant in the turbulent atmosphere

When a slightly divergent laser beam passes through a turbulent ground level atmosphere and strikes a linear grating, fluctuating self-images are formed at Talbot distances. By superimposing a similar grating on one of the self-images, even for the case of parallel gratings' lines, fluctuating moiré fringes are formed owing to the beam divergence. Recording the successive moiré patterns by a CCD camera and feeding them to a computer, after filtering the higher spatial frequencies, produces highly magnified fluctuations of the laser beam. Using moiré fringe fluctuations we have calculated the fluctuations of the angle of arrival and the atmospheric refractive index structure constant. The implementation of the technique is straightforward, a telescope is not required, fluctuations can be magnified more than ten times, and the precision of the technique is similar to that reported in our previous work.